This invention relates to locomotive windshield wiper systems, and more specifically to an electrically powered locomotive windshield wiper system incorporating a DC-DC electronic power convertor having a current source characteristic emulating a conventional vehicle battery so as to provide sufficient current to overcome high torque loads caused by snow, ice or other debris on a windshield.
Locomotive windshield wiper systems have historically been powered by pneumatic motors even though pneumatic motored wipers have several undesirable features. For example, pneumatic motored wipers are noisy to operate and the elevated noise can be heard in the locomotive operator""s cabin. Further, pneumatic wipers wipe in a sporadic, jerky motion and sometime stall in mid-sweep. Additionally, pneumatic wiper systems require two separate and independent controllers, one for the wipers and a second for a washer system. Still further, pneumatic wipers do not have capability for interval delay speeds. Because of these undesirable features, locomotive owners and builders would like to cease using pneumatic wipers.
A typical diesel-electric locomotive uses a relatively high voltage battery as compared to conventional vehicle systems. For example, a typical locomotive uses a 74 Vdc battery to supply suitable cranking power for a 4400 HP, 16 cylinder diesel engine. Use of this battery to power a windshield wiper system having conventional 12 volt DC motors presents several problems. The typical solution of using a dropping resistor to reduce voltage to the relatively low voltage DC motors is not desirable due to the excessive power consumption in the dropping resistor and the current limiting effect of the resistor when high currents are required to overcome high torque, or stalled, situations such as a snow-loaded windshield or when wiper blades were frozen to the glass. If the motor is unable to draw enough current to develop sufficient torque to clear the load, this system is unsatisfactory.
Conventional DC-to-DC power convertors for converting the 74 Vdc battery voltage to about 12 Vdc for the windshield wiper motor are also unsatisfactory. It is believed that existing power convertors, which could supply the expected steady state current, could not provide the high current required to drive a high torque load. More particularly, such convertors are designed to supply some nominal current at a tightly regulated voltage and are not capable of supplying substantially higher currents without their protective circuits effecting a shut down. While this problem could be overcome by providing a convertor with substantially higher nominal current capacity, the cost of such a high capacity convertor would be excessive. The reason for this is because power supply and convertor designers design power convertor with rigid voltage output characteristics, thus in stalled conditions, existing convertors would continue to maintain a constant voltage instead of allowing for an increase in current output from the convertor.
Towards this end, there is a particular need for a windshield wiper power system that can utilize electric power from a locomotive""s relatively high voltage battery, perform satisfactorily when the wipers experience high torque situations, produce less noise in the locomotive operator""s cabin, allow the washer system and wiper system to operate from the same controller, provide operation of the wipers at a variety of interval delay speeds and not have a cost which makes the system impractical.
A windshield wiper/washer system for a locomotive having a relatively high voltage power source comprising a first DC electric motor connected for driving a windshield wiper and a second DC electric motor connected for driving a windshield washer. A DC to DC power convertor having input terminals to receive power from the locomotive power source and being operative to convert relatively high voltage to relatively low voltage suitable for powering the first and second motors. The power convertor also has output terminals connected to supply DC electric power to the first and second DC electric motors. A controller is connected to enable operation of the motors. The converter, when operating, has a dynamic response characteristic that emulates the electric power characteristics of a conventional vehicle battery whereby the power convertor can be rated for supplying nominal motor current but can supply relatively high currents to the first DC motor to allow the motor to overcome stalled conditions.